Fluidised bed incinerators: thermal treatment with energy recovery

Indaver uses fluidised bed incinerators to treat non-recyclable industrial waste and sludge from industries and water purification. Rapid incineration allows the technology to process very large volumes. The energy from the incineration is converted into steam and electricity for use by Indaver and third parties.

Shipment

Trucks deliver the waste in bulk to the covered waste acceptance hall. The fixed waste is first shredded and deferrized in the pre-treatment installation, which consists of two identical production lines, each with two shredders and two overhead magnets.

Afterwards, the material is transferred to a common conveyer belt where it is deferrized again, and then deposited, via the waste conveyer belt, in one of the six tipping apertures into the waste bunker.

Sludge is dumped in one of the three sludge bunkers. A semi-automatic crane is used for mixing and feeding the sludge silo, from where the sludge is pumped into the furnaces.

Thermal treatment

Each furnace is equipped with two feeding propellers that dose the solid waste from the feeding chute onto the fluidised bed. The sludge is pumped into the furnace in an even and controlled manner.

The incineration process takes place in a strong rotating fluidised bed of sand at a minimum temperature of 850°C.

In addition to minimising the formation of dioxins and NOx (nitrogen mono-oxides), urea is injected into the furnace to reach the required emission ceilings of NOx.

Propellers remove the sand and bottom ashes from the furnace. Afterwards, the sand is sieved and subsequently brought into the fluidised bed again. A magnet removes the metals from the bottom ashes.

Energy recovery

Rational energy management was the focal-point in designing the fluidised bed installation. The furnaces are therefore built to recover energy efficiently. The heat generated from the thermal treatment is recovered in a vertical steam boiler. The steam produced is transferred to a turbine generator and converted into electricity, which is supplied to the public electricity grid.

The steam released during treatment will serve the heat network ECLUSE, which will begin supplying heat and steam to neighbouring businesses in the Waasland Port from autumn 2018.

Extensive gas washing

The flue gases are purified intensively to meet the strict emission standards. Electro filters remove the fly ashes. Lime is injected in the Circoclean reactor to capture chloride and sulphur components, while brown coal is added for the removal of heavy metals and dioxins. The baghouse filters separate the solid components.

If necessary, the residues of flue gas purification are first solidified and afterwards dumped into a Category 1 landfill. The final step in the cleaning of the flue gases is the removal of the rest of the chloride and sulphur components by means of wet washing. Continuous monitoring of the emissions guarantees that the purified flue gases that leave the chimneys comply with the strictest environmental standards.

Recovery of valuable raw materials

Pre-treatment in the fluidised bed incinerators removes the metal fraction from most of the delivered waste. This scrap fraction is cleaned in the pre-treatment unit for highly calorific waste in order to reuse it.